Chemical deposition apparatus

ABSTRACT

A vertical flow-type deposition apparatus, typically for growing semiconductor layers, including epitaxial layers, upon a large plurality of substrates at one time. These are carried, vertically disposed, upon the outside of a rotatable barrellike susceptor, while an induction heating coil is within the susceptor. Vapors or gases for processing are admitted at the bottom of a water-cooled enclosure and are exhausted at the top. The coil is separated from the processing volume by a refractory shield.

[ Feb. 29, 1972 United States Patent Hugle et a1.

3,424,629 1/1969 Ernst et al..... William B. Bugle, Palo Alto; Donald G.32 2; 33? 3' Pedrotti, Cupertino; William F. Perrine, 4/1 alasevtetam yCaplta 3,233,578 2/1966 Hugle Industries, 1nc., Sunnyvale, Calif. Man 5,1970 Primary ExaminerMorris Kaplan Attorney-Harry R. Lubcke 16,796

[54] CHEMICAL DEPOSITION APPARATUS [72] Inventors:

[73] Assignee:

[22] Filed:

Appl. No.:

ABSTRACT A vertical flow-type deposition apparatus, typically for grow-[51] 3 ing semiconductor layers. including epitaxial layers. upon a [58]Field large plurality of Substrates at one time. These are carriedvertically disposed, upon the outside of a rotatable barrellike 56]References Cited susceptor, while an induction heating coil is withinthe susceptor. Vapors or gases for processing are admitted at the bottomUNITED STATES PATENTS of a water-cooled enclosure and are exhausted atthe top. The coil is separated from the processing volume by arefractory 3,460,510 3/1969 shield 3,039,952 3,395,304

118/48 18/49 X 18/49 X 5 Claims, 2 Drawing Figures 6/1962 Fairchild et:11. l. 7/1968 HEAT Ag EXCHANGER As GENERATOR PAIENIIZDI'EB 29 I972 FIG.I;

SHEET 1 [IF 2 2 I I I I 4H I I I A. Z GENERATOR 2 33 I I III I IIIIIIII7 I IIII 28III HEAT EXCHANGER INVENTORS WILLIAM B. HUGLE DONALD G.PEDROTTI WILLIAM F. PERRINE AGENT PATENTEDFEBZQ 1912 SHEET 2 [IF 2 FIG.2.

INVENTORS WILLlAM B. HUGLE DONALD G. PEDROTTI WILLIAM F. PERRINECHEMICAL DEPOSITION APPARATUS BACKGROUND OF THE INVENTION This inventionrelates to high-temperature processing apparatus used for preparing thinfilms of semiconductor or dielectric materials useful in fabricatingsemiconductor devices.

The conventional reactor for semiconductor processing is of horizontalconstruction, with the substrates or wafers to be processed resting upona dishlike susceptor. An induction coil for heating surrounds thesusceptor outside of a horizontally disposed vacuumtight tube of quartz.

Pancake-type coils under a rotating horizontal susceptor within a belljar have been used in early so-called vertical reactors. Some verticalreactors have been known, but these have employed a fully externalheating coil of relatively large size. Such a coil must be removed eachtime the reactor is reloaded. This imposes certain difficulties inmaintaining batchto-batch uniformity of product, since it is difficultto reposition the coil in exactly the same position with exactly thesame turn-to-turn spacing for each batch.

Additionally, early vertical apparatus included an open-tothe-atmosphereexhaust aperture at the top of the bell jar. This precluded establishinga vacuum in the workspace and prevented a concomitant increase in theprecision of processing.

BRIEF SUMMARY OF THE INVENTION The invention is concerned with aprocessing reactor employing a vertically disposed cylindrical susceptorwith a helical heating coil internal to the susceptor. Normally, thesusceptor is rotated; by an external mechanical drive. This ispreferably coupled to the susceptor by a mechanical-magnetic drive,eliminating the need for a rotating vacuum seal.

Additionally. the coil is sealed from processing gases by a refractoryquartz liner, or coil-enclosing cylinder. This construction also reducesthe volume of such gases required to fill the reaction chamber. Thus,the composition of a gas can be changed more rapidly than in otherreactors holding the same number ofwafers.

A vertically upward gas flow pattern fosters uniformity of processing.

A cooled metal enclosure may be adjusted in temperature to avoidcondensation of reactant products upon the inner walls thereof.Moreover, this surface is easily cleaned.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view of theapparatus, in broken section along lines 1-1 in FIG. 2 to bestillustrate the structure.

FIG. 2 is a plan view of the same, also in section, and along lines 2-2in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, numeral 1 identifiesa vacuum baseplate. It is suitably supported at a convenient height forworking by known means not shown. Passing through the plate are pluralmeans to selectively introduce gaseous reactants into the workingvolume, these being entrance apertures 2. In general these may vary innumber and placement, but in exemplary apparatus four aperturesuniformly spaced (at 90) radially relatively central to the annularworking volume have been satisfactory.

It has been found desirable to water-cool the baseplate. This has beenaccomplished by an annular path 4 within the plate. The path has aradius approximately the same as the center of the working volume inorder to cool where the most heat is generated. The path may be formedby turning a circular groove central of the thickness of the baseplateand then forcing in enclosing ring 3 to provide a watertight channel.Suitable inlet and outlet holes are provided to accommodate the flow ofcooling medium, but these have not been shown for sake of clarity.

Cooled enclosure 5 is normally of cylindrical shape, with a closed domedtop to withstand external atmospheric pressure at such times as a vacuumis within the enclosure. The lower surface 6 of the enclosure ismachined flat so that a vacuumtight joint can be made with baseplate 1with the addition of known vacuum grease to aid the seal. An equivalentO-ring construction may also be used.

The enclosure is arranged for cooling by the provision of inner liner 7.A cooling fluid, typically water, is circulated within the space betweenthe enclosure and the liner by a nominal pressure from pump means notshown. The flow is between inlet 8 at the bottom of the structure andoutlet 9 at the top. It has been found desirable to form a spiral baffle13 of tubing to occupy the space between the enclosure and the liner ina spiral having perhaps five convolutions. The tubing is welded inplace. The cooling medium thus swirls upward around the cavity soformed, as desirable for uniform cooling.

Stainless steel is a suitable material for this structure. Aluminum isan alternate material. Typically, the interior of the liner is highlypolished to allow easy cleaning of any reactants that might depositthereon during the use of the apparatus, and to reflect the heat ofprocessing.

It has been found that usual cold tap water may be used for the coolingfluid; however, the possibility of condensation of reactants upon theinside of the liner 7 is then present. When the temperature of thisfluid is increased, to be somewhere between room temperature and thetemperature within the operating workspace 10, this possibility isgreatly reduced. An increase in temperature is accomplished by passingthe cooling fluid through heat exchanger 11. In this known device thetemperature of the fluid is regulated by thermostatically actuatedvalves which arrange an appropriate degree of recirculation of thefluid. The base cooling path 4 may be coupled into the exchanger coolingsystem, preferably at the cool (beginning) end thereof, or a separateflow of cool water may be provided. Suitable known hoses and fittingsare employed for completing the recirculation circuit through inlet 8,outlet 9, and coupling-in the path 4 if desired, and these have not beenshown.

Susceptor 12 is typically a right-cylindrical element having a lengthtwice its diameter and is formed of graphite. The whole apparatus may beconstructed in a wide variety of sizes and of some variation in shapeand materials of construction, but a length of 10 inches, diameter of 8inches, and a thickness of graphite of from to 1 inch may be considerednominal. The shape of this element gives rise to the term barrel reactorfor the whole apparatus. Equivalent shapes may also be used, such as atruncated conical section with limited conical slope to the outersurface.

The susceptor is normally machined and includes a large plurality ofrecesses or indentations 14. These carry the workpieces, substrates orsemiconductor wafers 20, by the workpieces simply resting in theindentations, necessarily at a slight inward angle at the top.

Uniformity of processing is a mark of excellence of any reactorapparatus. This is found to be exemplary herein if the inward-leaningindentations have an angle with the vertical of the order of 2 /2". Thisprovides enough slant to retain the wafers in place despite rotation ofthe susceptor and prevents a reduction of deposit at the top of eachwafer, particularly with certain reactants, such as silane (SiH Forother reactants, such as silicon tetrachloride (SiCl or trichrorosilane(SiHCl an angle to the vertical of the order of 7 is allowable.Uniformity of processing has been repeatedly measured and is within avery few percent of absolute uniformity.

Susceptors are usually provided for variously sized wafers orsubstrates, as 1 inch, l'rinch, 2 inch, or larger diameters. A maximumcapacity of 50 2-inch diameter wafers per susceptor in an exemplarymodel is typical. For greater capacity two susceptor-enclosure entitiesmay be employed with a common processing control system.

The susceptor is arranged for rotation to enhance uniformi ty ofprocessing. While this may be provided by a rotary vacuumtight joint atthe bottom of the apparatus, a magnetic drive has proven superior.Within the processing enclosure susceptor 20 stands upon refractorycylindrical support 27, say of quartz, which support thermally insulatesthe mechanism below from the often red-hot heat of the susceptor.Support 27, in turn, is supported upon driving ring 15, which is alsothe upper race of a ball bearing and retainer structure 19 and so thisring is made of hardened steel.

Equally spaced around driven ring 15 are a plurality of driven magnets16, such as eight. These are ofthe known highflux permanent magnet typeand are in the shape of a miniature horseshoe, with opposite poles atopposite extremities facing outward around the ring. These face anequivalent structure of driving magnets 17, facing inward, and drivingring 18, through stationary intermagnet membrane 28. The latter isfastened by welding to the inner cylindrical surface of baseplate ring38, which in turn is welded to baseplate 1, and to the outer surface ofstationary lower race 31. Membrane 28 is preferably formed of stainlesssteel. It is necessary that the membrane be vacuum tight and also towithstand atmospheric-to-vacuum pressure structurally.

The outer periphery of driving ring 18 is supplied with gear teeth,making it in effect a ring gear, as well as means for carrying drivemagnets 17 on its inner surface. Ring 18 is sup ported by plural rollers30, say three, which are attached to stationary lower race 31 by shafts32. This race also supports the whole susceptor rotating structurethrough balls 19 and also carries plural entrance apertures 2, of whichfour is a typical number. Selected gases and/or vapors are introducedinto working space of the apparatus for processing purposes throughapertures 2.

The gear on ring 18 is driven by pinion 33,.which is attached to motor34. With the speed reduction thus obtained the susceptor is rotated atselected speeds within the range of from 2 to 10 revolutions per minute(r.p.m.). Magnets 16 and 17 are oriented so that a north pole of one isopposite a south pole of the magnet facing it. Thus, there is strongmagnetic attraction and the inner rotating structure rotates at the samespeed as the outer one. Typically, the motor is supported from plate 1,but this and other nonvital supports have been omitted from the drawingsfor sake of clarity.

Refractory shield 21 is held stationary and vacuumtight by angle sealer35, which fits between it and stationary lower race 31. Coil support 36has a lower ring 37, which is attached to the lower surface of lowerrace 31. The upper extent of support 36 holds adjusting screws 25, aboutwhich more is stated later herein. Supports 36 need only be columnsunder each adjusting screw.

A distinct advantage of the structure of this apparatus is the reductionof working volume 10 to that required for processing alone. This isaccomplished by the inclusion of refractory shield 21. This shield istypically formed of quartz, of cylindrical shape and with an enclosingtop. It fits inside of susceptor 12 and is fastened in place by anglesealer 35. As has been mentioned, its presence allows the composition ofa gas to be changed more rapidly in processing than in other reactorsholding the same number of wafers. 7 Within the shield, heating coil 22is supported by upper clamps 23, which may be fastened to the shield orotherwise supported. At the bottom, coil 22 is supported by loweradjustable clamps 24, which, in turn, are supported by adjusting screws25. These screws are provided with round heads that are blind-anchoredin corresponding round recesses in supports 36. Square or hexagonalsections 26 are formed directly above the supports to allow rotation ofthe screws with a wrench or equivalent tool. The screws enter threadedholes within lower clamps 24, and when turned force the clamps upward ordownward, depending upon the direction of rotation of the screws. Allclamps 23 and 24 are preferably of electrical insulating material, orare otherwise arranged so that turns of the coil 22 will not be shorted.

This means of adjusting the position of helical coil 22 and the pitchbetween any or all of its convolutions allows maximization of theheating effect upon wafers 20. Typically, this is maximized foruniformity. By initially slightly deforming coil 22 axially, from normaluniformity between spacing of the turns, factors which act againstuniform heating of the work can be compensated for.

Coil 22 may be merely a resistance element and heat for processing thework obtained from PR loss of electric current caused to flow throughit. However, it is preferable that the coil induce heating by causingcurrent to flow in the electri cally resistive susceptor 12 and the FRloss thereof cause the heating. This is accomplished by supplying analternating current of high frequency to coil 22.

Accordingly, coil 22 is normally constructed of high-conductivitymaterial, such as copper, in tubular form. This form is as shown in theupper right sectioned part thereof in FIG. 1 and by the ellipse sectionin FIG. 2. Preferably a cooling fluid, typically water, is passedthrough the tubing of the coil. Suitable hydraulic connections areattached to each end thereof, but these have not been shown, and merelyconvey the fluid in one end of the coil and out the other by insulatinghose means that will not electrically short the coil.

It has been found that an alternating current having a frequency as lowas 10,000 Hertz may be used. This may be provided by AC generator 40 ofthe mechanically rotating type, such as is manufactured by the ToccoCorporation. A power output of 50 kilowatts is nominal. Because of thisrelatively low alternating current frequency the generator may belocated as far as 200 feet from the apparatus of this invention withoutappreciable electrical loss. The output of the generator is connected tothe extremities of coil 22, as is indicated by dotted connections 41 and42.

Exit aperture 3? communicates with the top of the operating workspace10, to allow exhausting vapor or gas reactants employed in variousprocessing steps that have entered the workspace through apertures 2.One exit aperture, essentially centered with respect to the workspace,has been found sufficient. Typically, aperture 39 is connected to avacuum pump, not shown, to rapidly exhaust volume 10 and to avoidcontamination thereof by any backflow of air. It will be understood thatthe number and the placement of entrance and exit apertures has aninfluence on the uniformity of processing and that this aspect has beenmaximized herein.

The various processes of epitaxial growth, cleaning, etching and dopingpossible in an apparatus of this type are known. As examples, epitaxialgrowth of silicon or germanium layers at precisely controlled rates, asby the reduction of silicon tetrachloride with hydrogen or the pyrolysisof silicon hydride, are possible. So also, hydrogen chloride etching,nitriding, oxidizing and carbiding, also surface catalyzed pyrolyticdeposition of metals or dielectric compounds.

In the matter of doping, P-type impurity concentrations can becontrolled over the range from 10 to 10 atoms per cubic centimeter, andN-type impurity concentrations from 10' to 10 atoms per cubiccentimeter.

The structure of the apparatus of this invention and the polished andhighly reflecting inner surface of inner liner 7 combine to minimize therequirement for heat exchanger 11. Thus, successful productionprocessing may be accomplished without it.

We claim:

1. A chemical deposition apparatus comprising;

a. an upstanding dual-walled enclosure (5,7),

b. a baffle (13) between the dual walls of said enclosure to directcooling fluid circuitously upward between said walls,

c. a single essentially cylindrical susceptor (12) having a verticallydisposed axis, and carrying a large plurality of substrates (20) to beprocessed, essentially vertically disposed upon the exterior of saidsusceptor,

d. annular magnetic means (15, 16) revolvably carrying said susceptorand disposed within the volume (10) of said enclosure (5,7

rotatable ring means (18) carrying plural circumferentially spacedmagnets (17) disposed adjacent to and in magnetic relation to saidmagnetic means, outside of the volume ofsaid enclosure,

. plural vertical inlet apertures (2) spaced one from the other only atthe bottom of said enclosure, said apertures being relatively concentricwith said cylindrical suscep tor, and

. a single exit aperture at the top of said enclosure relative- Theapparatus of claim 1 which additionally includes; a refractorycylindrical support (27) interposed between said magnetic means and saidsusceptor (12), to support said susceptor atop said magnetic means.

3. The apparatus of claim 1, in which;

a. said susceptor has a large plurality of recesses (14) each inclinedinwardly toward the top thereof approximately 2 for carrying saidsubstrates (20) upon said susceptor.

4. The apparatus of claim 1, which additionally includes;

a. a heat exchanger (11) connected to said dual-walled enclosure (5,7)to maintain the temperature of said cooling fluid at a selected valuesuited to inhibit deposition "of reactants upon the inner wall (7) ofsaid dual-walled container.

5. The apparatus of claim 1, which additionally includes;

a. a path (4) for cooling fluid within said baseplate (1) adjacent tosaid inlet apertures.

1. A chemical deposition apparatus comprising; a. an upstandingdual-walled enclosure (5,7), b. a baffle (13) between the dual walls ofsaid enclosure to direct cooling fluid circuitously upward between saidwalls, c. a single essentially cylindrical susceptor (12) having avertically disposed axis, and carrying a large plurality of substrates(20) to be processed, essentially vertically disposed upon the exteriorof said susceptor, d. annular magnetic means (15, 16) revolvablycarrying said susceptor and disposed within the volume (10) of saidenclosure (5,7), e. rotatable ring means (18) carrying pluralcircumferentially spaced magnets (17) disposed adjacent to and inmagnetic relation to said magnetic means, outside of the volume of saidenclosure, f. plural vertical inlet apertures (2) spaced one from theother only at the bottom of said enclosure, said apertures beingrelatively concentric with said cylindrical susceptor, and g. a singleexit aperture at the top of said enclosure relatively concentric withsaid cylindrical susceptor, whereby gaseous reactants admitted at saidplural inlet apertures flow upwardly past each of the rotatingsubstrates.
 2. The apparatus of claim 1, which additionally includes; a.a refractory cylindrical support (27) interposed between said magneticmeans (15) and said susceptor (12), to support said susceptor atop saidmagnetic means.
 3. The apparatus of claim 1, in which; a. said susceptorhas a large plurality of recesses (14) each inclined inwardly toward thetop thereof approximately 2 1/2 * for carrying said substrates (20) uponsaid susceptor.
 4. The apparatus of claim 1, which additionallyincludes; a. a heat exchanger (11) connected to said dual-walledenclosure (5,7) to maintain the temperature of said cooling fluid at aselected value suited to inhibit deposition of reactants upon the innerwall (7) of said dual-walled container.
 5. The apparatus of claim 1,which additionally includes; a. a path (4) for cooling fluid within saidbaseplate (1) adjacent to said inlet apertures.